Pretty hard. There's no true way of knowing when you're right. You can make educated guesses based on statistical likelihood of certain patterns, but nothing st

Pretty hard. There's no true way of knowing when you're right. You can make educated guesses based on statistical likelihood of certain patterns, but nothing stops people from constructing text that happens to look more "normal" when interpreted as another character set. If I see the bytes 0xE5 0xD1 0xCD 0xC8 0xC7, then it is a decent bet that it's intended to be مرحبا in DOS 708. But there's no definitive reason why it couldn't be σ╤═╪╫ (DOS 437) or åÑÍÈÇ (Windows-1252) or Еямих (KOI8-RU). Especially if you don't know for sure that the data is intended to be natural language. I can be pretty reasonably certain that it isn't, say, Japanese. 0xE5 in ShiftJIS is the first of a double-byte sequence, and it's odd, so the next byte would have to come from the range 0x40-0x9E, and 0xD1 does not fall within that range. In other words, it simply isn't valid ShiftJIS (it also isn't valid UTF-8). So you can narrow down the possibilities... but you're still making an educated guess. And you have to figure out a way to program that fuzzy, judgment-y analysis into software.